The invention generally relates to the selective deposition of graded materials, and more particularly, to the selective deposition of materials in such a way as to provide barrier coatings on certain portions of objects transported through a deposition chamber while leaving certain other portions of the objects uncoated.
Electroluminescent (“EL”) devices, which may be classified as either organic or inorganic, are well known in the graphic display and imaging arts. EL devices have been produced in different shapes for many applications. Inorganic EL devices, however, typically suffer from a required high activation voltage and low brightness. On the other hand, organic EL devices (“OELDs”), which have been developed more recently, offer the benefits of lower activation voltage and higher brightness in addition to simple manufacture, and, thus, the promise of more widespread applications.
An OELD is typically a thin film structure formed on a substrate such as glass, metal or plastic. A light-emitting layer of an organic EL material and optional adjacent semiconductor layers are sandwiched between a cathode and an anode. The semiconductor layers may be either hole (positive charge)-injecting or electron (negative charge)-injecting layers and also may comprise organic materials. The material for the light-emitting layer may be selected from many organic EL materials. The light emitting organic layer may itself consist of multiple sublayers, each comprising a different organic EL material. State-of-the-art organic EL materials can emit electromagnetic (“EM”) radiation having narrow ranges of wavelengths in the visible spectrum. Unless specifically stated, the terms “EM radiation” and “light” are used interchangeably in this disclosure to mean generally radiation having wavelengths in the range from ultraviolet (“UV”) to mid-infrared (“mid-IR”) or, in other words, wavelengths in the range from about 300 nm to about 10 micrometer. To achieve white light, prior-art devices incorporate closely arranged OELDs emitting blue, green, and red light. These colors are mixed to produce white light.
Conventional OELDs are built on glass substrates because of a combination of transparency and low permeability of glass to oxygen and water vapor. A high permeability of these and other reactive species can lead to corrosion or other degradation of the devices. However, glass substrates are not suitable for certain applications in which flexibility is desired. In addition, manufacturing processes involving large glass substrates are inherently slow and, therefore, result in high manufacturing cost. Flexible plastic substrates have been used to build OELDs. However, these substrates are not impervious to oxygen and water vapor, and, thus, are not suitable per se for the manufacture of long-lasting OELDs. In order to improve the resistance of these substrates to oxygen and water vapor, alternating layers of polymeric and ceramic materials have been applied to a surface of a substrate. It has been suggested that in such multilayer barriers, a polymeric layer acts to mask defects in an adjacent ceramic layer, and therefore provides a tortuous pathway to reduce the diffusion rates of oxygen and/or water vapor through the channels made possible by the defects in the ceramic layer. However, an interface between a polymeric layer and a ceramic layer is generally weak due to the incompatibility of the adjacent materials, and the layers, thus, are prone to be delaminated.
Organic electronics may supplant conventional silicon-based technology if they can be manufactured for large area electronic devices at a much lower cost. Examples of low-cost electronic technologies include organic light-emitting devices (OLEDs), organic photovoltaic devices, thin-film transistors (TFTs) and TFT arrays using organic and solution-processible inorganic materials, and other more complicated circuits. Other electronic technologies include liquid crystal devices (LCDs), photovoltaic cells, electrochromic devices, and electrophoretic devices. Such electronic technologies are conventionally manufactured using predominantly batch-mode semiconductor fabrication processes. Such processes do not, however, fulfill the promise of low cost and large area potential. Thus, considerable research effort is being directed to fabricating organic electronic devices using printing processes on roll-to-roll compatible, mechanically flexible substrates. For example, Konarka Technologies Inc. has developed a photovoltaic cell manufacturing process that allows printing photo-reactive materials onto flexible plastic substrate in continuous roll-to-roll (R2R) fashion, similar to how newspaper is printed on large rolls of paper. Konarka's R2R manufacturing process enables production to scale easily and results in significantly reduced costs over previous generations of solar cells. See, for example, U.S. patent application publication 2003/0192584. SiPix Imaging Inc. has developed a R2R manufacturing process that produces large arrays of microscale containers on a flexible plastic substrate that may be used to fabricate ultra-low power, high contrast electrophoretic display devices (electronic paper). See, for example, U.S. Pat. No. 6,873,452.
OLEDs represent the most advanced of current organic electronic technologies as evidenced by the fact that OLED display products are now commercially available. However, these products are still manufactured using predominantly batch-mode conventional semiconductor fabrication processes and so have still not demonstrated the low cost and large area potential of organic electronics. A key impediment for this effort is the lack of availability of a mechanically flexible substrate that fulfills all the requirements for a functional OLED device. Further, commercial OLED devices use glass substrates and glass or metal encapsulation with epoxy seals and desiccants. These processes provide both low throughput and high cost.
To meet the stringent requirements put forth for the design of OLEDs and other organic electronic devices on flexible or inflexible substrates, a robust coating design should be realized which avoids easy defect pathways for permeation. Multilayer barrier structures including multiple sputter-deposited aluminum oxide inorganic layers separated by polymer multilayer (PML) processed organic layers have demonstrated promising moisture permeation rates in the range of 10−6-10−5 g/m2/day. It is commonly understood that organic layers may decouple defects in the inorganic layers and prevent the propagation of the defects from one inorganic layer to the other inorganic layers. In other words, the multilayer stack stops defects from propagating in the vertical direction through the coating thickness. A modeling study suggests that this defect decoupling forces a tortuous path for moisture and oxygen diffusion, and thus reduces the permeation rate by several orders of magnitude. Another study suggests that the inorganic-organic multilayer stack leads to higher performance through a transient rather than steady-state phenomenon. Regardless of mechanism, the multilayer barrier stack approach appears to be capable of yielding the required level of performance for OLED applications.
One potential limitation of the multilayer stack approach is that this type of structure tends to suffer from poor adhesion and delamination especially during thermal cycles of the OLED fabrication processes, since the inorganic and organic layers have sharp interfaces with weak bonding structure due to the nature of the sputter deposition and PML processes.
Therefore, there is a continued need to provide, in a continuous process, protective coatings over certain portions of the electronic devices, while leaving other portions of the electronic technology uncoated.